DE1769028A1 - Biaxially oriented polypropylene film - Google Patents

Description

KALLE AKTIENGESELLSCHAFT 1769028 Unsara Zalchan day sheet

K 1821 / Gbr: 366 ¹ PP-Dr.S-in March 20, 1968

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KALLE AKTIEHGESELLSCEAPT Wiesbaden-Riebrich

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Biaxially oriented polypropylene film

The present invention relates to a biaxially oriented film of isotactic polypropylene with improved Adhesive properties.

Isotactic polypropylene films packed in a or in two mutually orthogonal directions by stretching below their crystallite melting point are oriented, are suitable because of their mechanical strength, their optical clarity and their surface gloss and their good water vapor density for many areas of application.

A major disadvantage of the film, however, is due to the non-polar character of the material and its high density Molecular orientation caused poor adhesion, for example to heat-sealing layers, metal layers

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K 1821 / Gbir. 366 ¹ PP-Dr.S-iir 2O.3.6B έ

or similar.

Polyethylene or so-called hotmelts as well as copolymers based on vinyl acetate, vinyl chloride and nitrocellulose are usually used as the kiss-sealing layers. If one also wants to achieve good barrier properties of the composite film against gases such as COp and O ₂ , a requirement that is placed on the packaging film to an ever greater extent, the oriented polypropylene film is provided with hot-melt layers based on copolymers of vinylidene chloride. As a rule, aluminum is used for pure metallization of the foils, for example by vapor deposition, while copper, silver or gold are used for special applications.

There are numerous processes that surface the biaxially stretched isotactic polypropylene film for subsequent coatings or metallizations to make it more suitable, such as the treatment of the foils with electrical discharges in air or more specifically. Gasati'iosphciren, with purely chemical processes or flame treatment. The surfaces pretreated in this way result in satisfactory composites with copolymers based on vinylidene chloride, vinyl chloride or

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_ Our · sign day sheet

K 1821 / Gbm 366 ¹ FP-Dr.S-im 20.3-68 /

Vinyl acetate when applied from suitable organic solvents.

3e layers made from organic solution have significant procedural disadvantages ; they require, for example, precautions to avoid the risk of explosion! and the removal or recycling of the solvents used. In addition, the heat-sealing layers produced in this way do not have any antistatic properties and can be physiologically questionable. In the important case of the heat-sealing layer based on vinylidene chloride, the barrier properties are not entirely satisfactory.

For the reasons mentioned, there is a tendency to apply the heat-sealing layers from an aqueous dispersion. Here, however, the adhesion of the coating to the carrier film is in spite of intensive surface pretreatment unsatisfactory for most requirements. This has hitherto been used to counter this difficulty net that on the one hand the carrier film by adding polyethylene or copolymers of polypropylene and polyethylene or mixtures of polyethylene with polypropylene modified in such a way that the following Coatings resulted in better bond strengths.

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KALLE AKTIENGESELLSCHAFT 1769028

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K I821 / Gbm 366 ¹ PP-Dr.S-im 20.3.68

On the other hand, additional adhesion was applied to the pretreated surface for the purpose of further improving the adhesion a so-called base or adhesive coat made of aqueous dispersion or organic solution on which then In a second step, the actual heat-sealing layer is applied with the required properties became.

Overall, the additional application of the adhesive coat from organic solution already results the above-mentioned procedural disadvantages and the application from aqueous dispersion only relatively good bond strengths, which, however, are not sufficient for all applications.

In addition, the modification of the homopolymeric isotactic polypropylene leads to copolymers or the • Adding copolymers or polyethylene in any case to a greater or lesser degree of impairment the optical qualities of the polypropylene carrier film and also causes minor changes in the Modulus of elasticity.

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K 1821 / Gbm 366 ¹ PP-Dr.S-im 20.3-68

Our · Zfldien Tag 'sheet

From the foregoing, the compromises that have been necessary so far can be seen, all of which are from the bad ones Adhesion of the layers to the biaxially stretched polypropylene surface arise.

The invention is based on the object of developing a biaxially oriented isotactic polypropylene film, the surface of which has been changed in such a way that the subsequently applied coatings appear better adhere to her.

The solution to this problem is a biaxially oriented film made of isotactic polypropylene, which is coated on at least one side with a layer of an isotactic polypropylene or a mixture of isotactic polypropylene with up to 15 % by weight, based on the total polymer, of atactic polypropylene or a mixed or copolymer of propylene is provided with up to 15 wt.i, based on the total polymer, of ethylene, which is essentially reoriented,

Erfindupgsgemäß usable are isotactic polypropylene · Rait densities in the range 0.880 to 0.920 and melt indices i, - at 23O ⁰ C between k and

100 g / 10 min, preventively 10-50 g / 10 min, measured 109888/1743

KALLE AKTIENGESELLSCHAFT 1769028 Our · ZrtdMfi day sheet

K 1821 / Gbm 366 ¹ FP-Dr.S-im 20.3-68 /

according to ASTM D 1238-57 T.

Mixtures of isotactic polypropylene with up to 15 wt /? Are obtained as coating materials on the total polymer, on atactic polypropylene or! lisch- or copolymers of propylene with up to to 15% by weight, based on the total polymer Ethylene used. However, an isotactic polypropylene is advantageously used with the same or a different flow behavior than that used for film production. Particularly preferred however, one and the same isotactic polypropylene is used for the production of film and coating.

The composite consists of an arbitrarily thick biaxially oriented base film of isotactic polypropylene, at least on one side a coating of the above-described polymers or copolymers mixed with a thickness of 0.2 to k ^ m, preferably 0.5 to 1.5 / um , owns.

The composite film according to the invention is produced in such a way that in the process known per se for the biaxial stretching of films made of isotactic polypropylene, sum example with the aid of 109886/1743

KALLE AKTIENGESELLSCHAFT 1769028 Our «Zalditn day Matt

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so-called frame stretching process, after the first stretching step j which is preferred in the present case is carried out in the longitudinal direction, on the monoaxially stretched film, optionally after an adhesion-improving film Pretreatment, a layer of 1-20 / µm, preferably 3-10 / µm, extruded on one or both sides and stretches this VerbuVid in the direction orthogonal to the first stretching step. If necessary the coating can be done with different polymers on both sides.

The composite film according to the invention can then in surface-treated in the same operation or after intermediate storage by one of the known processes and provided with a layer on one or both sides. So can a layer of a heat sealable Material, for example a polyvinylidene chloride copolymer from an aqueous dispersion, applied, the composite dried and wound up.

Surprisingly, the heat sealable produced in this way shows Film significantly improved adhesion of the heat seal layer to the inventive film Foil. An additional anchoring layer is not necessary

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KALLE AKTIENGESELLSCHAFT 1769028 Under · ZrtdMtt Tag Btcrtt K 1821 / Gbm 366 ¹ PP-Dr. S-iin 3/20/68

themselves. Furthermore, the method can be carried out much more easily. For example, isotactic polypropylene is extruded onto a monoaxially stretched film made of isotactic polypropylene without any difficulty. In addition, the good optical properties of the base film are retained.

The qualitative and procedural precautions of the • heat sealable film produced according to the invention are to be explained in more detail using the following examples in conjunction with the accompanying drawings.

The assessment of the properties of the coated films mentioned in these examples is as follows

Measurement methods are based on:

a) The seal strength is determined on a 1 cm wide strip that runs across the seal seam of the Sample has been cut out. The measure of the seal strength is the force in p / cm strip width, which is measured during separation with a feed rate of 200 rara / min on a tear-off device.

The clamped free ends of the specimen should be one with the film that has not yet been separated

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KALLE AKTIENGESELLSCHAFT 1769028 Under »Z» ldi »n Tag sheet

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Form an angle of approx. 90 °. The sealing seam with a width of 15 mm was produced on a pneumatic sealing device under the constant conditions of 120 ^° C., 2 seconds and 1.3 kp / cm.

b) Seal strength after 5 minutes of boiling

Testing of the sealing strength described under a) after immersion of the sample in boiling V / ater for 5 minutes.

c) In the measurement of bond strength of a polypropy len / polyethylene composite, the procedure is that the composite film of the polyethylene side is cut so that the polypropylene is not violated. The loosened bond is opened 15 mm, and then 10 mm wide strips are cut. The bond strength is then measured in Τ-Ρ ·· 1 at a feed rate of 100 mm / min with a conventional device.

d) The adhesion of the metal layer was determined as follows;

^{25 tesafilm 104 M,} which was then wide, was rolled onto the metal layer with a force of 2.5 kp with the aid of a roller (diameter Ho mm)

109886/1743 original

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Ukmi « ZeUm * Day sheet

K 1821 / Gbm 366 ¹ PP-Dr.S-im 20.3.68 VÖ

to

Composite has now been opened and in two clamps clamped, on which a Kraftmeßvorrichtunc was connected. Then the composite was with increasing feed speed of 2.5 mm / sec Pulled apart up to 150 mm / sec in the T-peel. The force at which began to detach the metal layer from the polypropylene film and stuck to the "tesa film".

example 1

I3otaktisches polypropylene having a density 0.91 with the Heltindex i, - at 23O ⁰ C of 15 g / 10 min, measured according to ASTM D 1238-57 T, and was extruded at a ratio of X = 6.0 in ₁ li "5 ° C stretched lengthways. The thickness of the longitudinally stretched film 2 (FIG. 1) was 200

Was thereto at a speed of 60 m / min on both sides of a 28O ⁰ C hot melt 1, 3 (Figure 1) in a thickness of approximately 6 to coated from the above-described polypropylene to the uniaxially stretched polypropylene film and the composite at 25 ° C cooled. Thereafter, the film was ^s q at a draw ratio of 8.0 and Λ transversely stretched to a stretching temperature of about 165 ⁰ C. A biaxially oriented 25 / μm thick film 5 (FIG. 2) was obtained, which

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KALLE AKTJENGESELLSCHAFT Π69028 Unj «f» Z «kh« n day Hott

K 1821 / Gbm 366 ¹ PP-Dr.S-im 20.3.68 U

was coated on both sides with only insignificantly oriented isotactic polypropylene in about 0.8 μm thickness k.6 (FIG. 2).

The film was then passed through an electrical discharge and coated with an aqueous dispersion a polyvinylidene chloride copolymer of 90Ϊ Vinylidene chloride and 10 * acrylonitrile and acrylic acid ester coated on both sides in a dry layer thickness of 3 / Ua, dried in a hot air tunnel at 120 ° C and wound up.

The sealable film produced in this way had the following properties:

Heat seal strength: 120-1 * 0 p / cm

Heat seal strength after 5 rain cooking IkQ p / cm

A comparison film produced by the same process, but without the isotactic coating Polypropylene after longitudinal stretching had the following properties: Heat seal strength: 30-50 ρ / cm

Heat seal strength after 5 minutes of cooking: 30-50 p / cm

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KALLE AKTIENGESELLSCHAFT 1769028 Urns Ζ · Ι * βη To «BIoR

K 1821 / Gbm 366 ¹ PP-Dr.S-im 20.3.68

Example 2

A heat-sealable film was produced analogously to Example 1. In addition, the longitudinally stretched polypropylene film was treated with an electrical discharge prior to extrusion coating. It was found the following characteristics:

Heat seal strength : 100-150 p / cm

Heat seal strength after 5 minutes of cooking: 120-140 p / cm

Example 3

A heat-sealable film was produced, again as described in Example 1, but with the difference that, in addition to the treatment with an electrical discharge, the longitudinally stretched film was only cooled to 10O ⁰ C, extrueionsbe coated at this temperature and then fed to the transverse stretching. The resulting values were as follows: Heat seal strength: 120-160 p / cm

Heat seal strength after 5 minutes of cooking: 130-150 p / cm

Example 4

An elongated film made of isotactic polypropylene with the physical properties described in Example 1 was coated on one side with the same isotactic polypropylene in a thickness of about 6

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K 1821 / Obm 366 ¹ FP-Dr.S-im 20.3.68

extrusion coated with 10 wt% atactic polypropylene of density. were added to 0.86. The film obtained after the second stretching was provided with a heat-sealable layer analogously to Example 1, for which the following characteristics were determined:

Heat seal strength: 120-140 p / cm

Heat seal strength after 5 minutes of cooking: 120-140 p / cm

Example 5

A sheet of isotactic polypropylene stretched longitudinally according to Example 1 was extrusion coated on one side with a layer of 4 μm isotactic polypropylene with the same properties as in Example 1 and a layer of 16 μm polyethylene with a density of 0.918 using a corresponding two-substance nozzle, in such a way that the polypropylene layer lay between the elongated polypropylene film and the polyethylene layer. This composite was cross-stretched at l60 ° C with a draw ratio} \ 8.0 and rolled up.

In contrast to the usual determination of the heat seal strength has been made to more precisely determine the bond strength of the polyethylene layer on the polypropylene layer

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KALLE AKTIENGESELLSCHAFT 1769028

- Our · Zafdian day sheet

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To be able to measure the composite film produced in this way additionally on the polyethylene side with 75 to polyethylene the density 0.918 extrusion coated to the To have the opportunity to peel off the polyethylene layer without tearing off.

The bond strength was

30-40 p / cm,

while a correspondingly produced composite without the polypropylene intermediate layer has a bond strength from 15-20 p / cm

exhibited.

Example 6

A biaxially stretched polypropylene film produced analogously to Example 1 was subjected to a high vacuum in a known manner with aluminum.

The bond between the metallization and the polypropylene film was

400 ρ / cm,

while a correspondingly produced composite without the polypropylene intermediate layer has a composite adhesion from 240 p / cra

exhibited.

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Claims (3)

KALLE AKTIENGESELLSCHAFT 1769028 Our mark day sheet K 1821 / Gbm 3661 PP-Dr.S-im 20.3.68 patent claims 1. Biaxially oriented film made from isotactic polypropylene with improved adhesive properties, characterized in that they are at least one side with a layer of an isotactic polypropylene or a mixture of isotactic polypropylene with up to 15 wt. *, based on the total polymer, of atactic polypropylene or a mixed or Copolymer of propylene with up to 15 Gew.Jf, based on the total polymer, of ethylene that is essentially unoriented. 2. Biaxially oriented film according to claim 1, characterized in that the layer of the same isotactic Polypropylene like the film is made. 3. Biaxially oriented film according to claims 1 and 2, characterized in that the substantially unoriented Layer has a thickness of 0.2 to 4 µm. 109886/1743 Ai ₆ Blank page COPY